Multiple sclerosis (MS) is a chronic disease of the central nervous system (CNS) characterized by multifocal regions of inflammation and myelin destruction. Typically, MS runs a protracted clinical course lasting over several decades with episodes of exacerbation followed by variable periods of remission. Available evidence indicates that the cause of MS is multifactorial and includes the genetic background of the individual as well as environmental influences, e.g. viral infection. The development of animal models in which the clinical and histologic pathology is similar to that observed in the majority of MS patients is imperative in order to attempt to better understand the underlying pathological mechanisms contributing to MS. Viral models of demyelination are important tools for studying the pathogenesis of disease. Persistent infection of mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) or Theiler's murine encephalomyelitis virus (TMEV) is characterized by axonal damage and ongoing demyelination mediated by inflammatory T cells and macrophages, which is similar both clinically and histologically to the human demyelinating disease MS. Combined with the fact that an environmental agent such as a virus is considered to be a contributing cause of MS, the JHMV and TMEV systems offer excellent models in which to study both the underlying pathological mechanisms that may drive demyelination in MS patients as well as novel therapeutic methods for promoting remyelination. Axonal damage is a key feature in the pathogenesis of MS. Following CNS infection with either JHMV or TMEV, there is extensive axonal damage that often precedes immune cell infiltration and demyelination. Understanding the molecular/cellular mechanisms by which axonopathy occurs in response to viral infection of the CNS will aid in uncovering novel ways to promote axonal sparing. Along these lines, employment of neural progenitor cells (NPCs) offers an attractive approach to both protect axons and initiate remyelination. We have determined that intraspinal transplantation of mouse NPCs into JHMV-infected mice with established demyelination results in improved clinical outcome associated with the differentiation of NPCs into oligodendroglia, extensive axonal sparing and remyelination. Our new results demonstrate that engrafted NPCs physically engage axons resulting in axonal preservation and remyelination. This proposal will interrogate (i) the molecular and cellular mechanisms resulting in axonopathy following viral infection of the CNS and (ii) mechanisms associated with NPC-mediated axonal preservation and remyelination.